#include <iostream>
#include <cstring>
#include <queue>

using namespace std;

const int N = 1e5 + 10;


int n, m;
int e[N], ne[N], h[N], idx;
int d[N];

void add(int a, int b) {
    e[idx] = b, ne[idx] = h[a], h[a] = idx ++ ;
}

int bfs() {
    memset(d, -1, sizeof d);
    
    queue<int> q;
    d[1] = 0;
    q.push(1);
    
    while (q.size()) {
        auto t = q.front();
        q.pop();
        
        for (int i = h[t]; i != -1; i = ne[i]) {
            int j = e[i];
            if (d[j] == -1) {
                d[j] = d[t] + 1;
                q.push(j);
            }
        }
    }
    
    return d[n];
}

int main() {
    cin >> n >> m;
    memset(h, -1, sizeof h);
    for (int i = 0; i < m; ++ i) {
        int a, b;
        scanf("%d%d", &a, &b);
        add(a, b);
    }
 
    cout << bfs() << endl;
 
    return 0;   
}